A category for Sparrow that allows setting the repeat total time and repeat start values of properties.

SPTween+RepeatValues.h

//
//  SPTween+RepeatValues.h
//  Sparrow 2.X
//
//  Created by Shilo White on 8/3/13.
//

#import "SPTween.h"

@interface SPTween (RepeatValues)

@property (nonatomic, assign) double repeatTotalTime;

- (void)animateProperty:(NSString*)property targetValue:(float)endValue repeatStartValue:(float)repeatStartValue;

@end

SPTween+RepeatValues.m

//
//  SPTween+RepeatValues.m
//  Sparrow 2.X
//
//  Created by Shilo White on 8/3/13.
//

#import "SPTween+RepeatValues.h"
#import "SPTransitions.h"
#import "SPTweenedProperty.h"
#import <objc/runtime.h>

#define TRANS_SUFFIX  @":"

typedef float (*FnPtrTransition) (id, SEL, float);

@interface SPTweenedProperty (RepeatValues)

@property (nonatomic, assign) NSNumber *repeatStartValue;

@end

@interface SPTween () {
    id _target;
    SEL _transition;
    IMP _transitionFunc;
    NSMutableArray *_properties;
    
    double _totalTime;
    double _currentTime;
    double _delay;
    
    int _repeatCount;
    double _repeatDelay;
    BOOL _reverse;
    int _currentCycle;
    
    SPCallbackBlock _onStart;
    SPCallbackBlock _onUpdate;
    SPCallbackBlock _onRepeat;
    SPCallbackBlock _onComplete;
}

@end

@implementation SPTween (RepeatValues)

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wobjc-protocol-method-implementation"

- (id)initWithTarget:(id)target time:(double)time transition:(NSString*)transition
{
    if ((self = [super init]))
    {
        _target = target;
        self.repeatTotalTime = _totalTime = MAX(0.0001, time); // zero is not allowed
        _currentTime = 0;
        _delay = 0;
        _properties = [[NSMutableArray alloc] init];
        _repeatCount = 1;
        _currentCycle = -1;
        _reverse = NO;
        
        // create function pointer for transition
        NSString *transMethod = [transition stringByAppendingString:TRANS_SUFFIX];
        _transition = NSSelectorFromString(transMethod);
        if (![SPTransitions respondsToSelector:_transition])
            [NSException raise:SP_EXC_INVALID_OPERATION
                        format:@"transition not found: '%@'", transition];
        _transitionFunc = [SPTransitions methodForSelector:_transition];
    }
    return self;
}

- (void)setRepeatTotalTime:(double)repeatTotalTime
{
    objc_setAssociatedObject(self, @"repeatTotalTime", [NSNumber numberWithDouble:repeatTotalTime], OBJC_ASSOCIATION_RETAIN);
}

- (double)repeatTotalTime
{
    return [objc_getAssociatedObject(self, @"repeatTotalTime") doubleValue];
}

- (void)animateProperty:(NSString*)property targetValue:(float)endValue repeatStartValue:(float)repeatStartValue
{
    if (!_target) return;
    
    SPTweenedProperty *tweenedProp = [[SPTweenedProperty alloc] initWithTarget:_target name:property endValue:endValue];
    tweenedProp.repeatStartValue = [NSNumber numberWithFloat:repeatStartValue];
    [_properties addObject:tweenedProp];
}

- (void)advanceTime:(double)time
{
    if (time == 0.0 || (_repeatCount == 1 && _currentTime == _totalTime))
        return; // nothing to do
    else if ((_repeatCount == 0 || _repeatCount > 1) && _currentTime == _totalTime)
        _currentTime = 0.0;
    
    double previousTime = _currentTime;
    double restTime = _totalTime - _currentTime;
    double carryOverTime = time > restTime ? time - restTime : 0.0;
    _currentTime = MIN(_totalTime, _currentTime + time);
    BOOL isStarting = _currentCycle < 0 && previousTime <= 0 && _currentTime > 0;
    
    if (_currentTime <= 0) return; // the delay is not over yet
    
    if (isStarting)
    {
        _currentCycle++;
        if (_onStart) _onStart();
    }
    
    float ratio = _currentTime / _totalTime;
    BOOL reversed = _reverse && (_currentCycle % 2 == 1);
    FnPtrTransition transFunc = (FnPtrTransition) _transitionFunc;
    Class transClass = [SPTransitions class];
    
    for (SPTweenedProperty *prop in _properties)
    {
        if (isStarting) prop.startValue = prop.currentValue;
        float transitionValue = reversed ? transFunc(transClass, _transition, 1.0 - ratio) :
        transFunc(transClass, _transition, ratio);
        prop.currentValue = prop.startValue + prop.delta * transitionValue;
    }
    
    if (_onUpdate) _onUpdate();
    
    if (previousTime < _totalTime && _currentTime >= _totalTime)
    {
        if (_repeatCount == 0 || _repeatCount > 1)
        {
            if (_currentCycle == 0)
            {
                _totalTime = self.repeatTotalTime;
                for (SPTweenedProperty *prop in _properties)
                    if (prop.repeatStartValue)
                        prop.startValue = [prop.repeatStartValue floatValue];
            }
            
            _currentTime = -_repeatDelay;
            _currentCycle++;
            if (_repeatCount > 1) _repeatCount--;
            if (_onRepeat) _onRepeat();
        }
        else
        {
            [self dispatchEventWithType:SP_EVENT_TYPE_REMOVE_FROM_JUGGLER];
            if (_onComplete) _onComplete();
        }
    }
    
    if (carryOverTime)
        [self advanceTime:carryOverTime];
}

#pragma clang diagnostic pop

@end

@implementation SPTweenedProperty (RepeatValues)

- (void)setRepeatStartValue:(NSNumber *)repeatStartValue
{
    objc_setAssociatedObject(self, @"repeatStartValue", repeatStartValue, OBJC_ASSOCIATION_RETAIN);
}

- (NSNumber *)repeatStartValue
{
    return objc_getAssociatedObject(self, @"repeatStartValue");
}

@end